1. Field of the Invention
The present invention relates to a liquid discharge head which discharges a liquid, specifically to an ink jet recording type of ink jet recording head which discharges ink to a recording medium to perform recording. Particularly, the invention relates to an ink jet recording head in which a shape of a discharged ink droplet is improved to enhance print performance and image quality by improving a structure of a liquid channel.
2. Description of the Related Art
In a thermal drive type used in the ink jet recording type, the liquid near a heating resistive element is instantaneously boiled by applying voltage to the heating resistive element, and the droplet is discharged by bubbling pressure generated due to a phase change in liquid. The liquid discharged from a discharge port forms a droplet by surface tension, and the liquid forms an image on a predetermined recording medium.
After the liquid is discharged, the droplet having an amount according to a volume of the discharged droplet is refilled from an ink tank through an ink supply port and an ink channel.
The liquid is not a spherical droplet but a columnar shape including a large main droplet portion and a long and thin tail portion immediately after the liquid is discharged from the discharge port of the printhead described above. The liquid column breaks apart into plural droplets by the surface tension of the liquid during a procedure in which the liquid column flies toward the recording medium from the discharge port. In the most general mode, the liquid column is divided into the main droplet portion and the tail portion, and then the tail portion is further divided into satellite droplets by the surface tension.
When the satellite droplets adhere to the recording medium, there is a problem that the satellite droplets become noises to prevent fine image formation. Recently the influence of the problem is increasing as the discharged main droplet portion is decreased. Furthermore, because the satellite droplet is extremely small, after the satellite droplet floats in air by the influence of air resistance or an air flow, the satellite droplet adheres to the ink tank or a printer main body, which results in a problem that the satellite droplet soils a hand of a user. Additionally, there are also possibly generated problems such that a sheet feeder malfunction is generated by the adhesion of the satellite droplets to an encoder, and such that printer main body breakdown is generated by the adhesion of the satellite droplets to an electric substrate.
The satellite is reduced by decreasing a droplet tail during the ink discharge.
U.S. Pat. No. 6,561,631 discloses a method of decreasing the droplet tail. According to the method disclosed in U.S. Pat. No. 6,561,631, in the ink discharge procedure from the bubble generation to the ink droplet separation, the ink going toward the discharge port by the bubble growth and the ink in the ink channel are blocked by the bubble, and only the ink isolated near the discharge port is discharged. Therefore, the generation of the droplet tail is suppressed.
However, in the technique disclosed in U.S. Pat. No. 6,561,631, because flow resistance is enhanced in a part of the ink channel in order to obtain the above-described effect, sometimes it takes a long time to refill the ink after the ink discharge, namely sometimes so-called refill characteristics become worsened. Therefore, it is difficult that the satellite generation is suppressed while a discharge frequency not lower than 15 kHz, which corresponds to recently demanded high-speed print, is maintained.